Pomarine Jaeger - leg injury?

Richard Bradus

By now many have had a chance to see the Pomarine Jaeger hanging out at Ocean Beach. I'm surprised that no one has mentioned the appearance of its left leg.

I was able to observe this individual at close range, and multiple excellent photos by others also show a clearly abnormal and enlarged tibio-tarsal joint (what we would call a knee on mammals, but actually more analogous to an ankle, at the mid point of the leg). There is an obvious pinkish protuberance anteriorly from what I presume to be the proximal aspect of the tarsometatarsus. Is this a healing fracture? Perhaps an infection? Whatever it is, it may explain in part the unusual behavior of this bird; spending a lot of time on the beach may be its way of trying to recuperate (?). It does appear to favor this leg - I did not see the bird walk, and when taking flight the leg dangles a bit and the bird takes some time to finally tuck it under its body. 

Any veterinarians or bird rescue folks out there who could provide an opinion or more definitive explanation?

Richard Bradus
San Francisco